We have designed and built an apparatus capable of making measurements of kinetic parameters of reactions involving redox active species. This pulse-injection rapidly stirred reactor has been tested using the reaction between an iron imidazole complex and hydrogen peroxide. We are currently using it to study photoelectrochemical rates which are of analytical importance. We have designed and built an apparatus which will be capable of detecting small quantities (sub nonomolar) of photoelectrochemically active species. This apparatus has been designed to minimize potential interferences from constituents of body fluids. This apparatus has not been exhaustively tested.